This invention pertains to a method for separating a product piece from one or more waste pieces. This invention also pertains to a method for cutting and separating pieces of glass. This invention also pertains to a method for making a glass substrate for use in magnetic disk manufacturing.
Japanese laid open patent publication 2-92837 discusses a method for cutting and separating a planar glass work piece into a product piece and a waste piece. During the 2-92837 method, the following steps are performed:
1. A circular scribe line is mechanically formed in a circular glass work piece to define a circular waste piece within the glass work piece.
2. The glass work piece is heated from the side containing the scribe line to propagate a crack from the scribe line into the interior of the work piece.
3. The glass work piece is heated a second time from the opposite side. This causes the crack to further propagate into the work piece.
4. A brass chilling tool is cooled by bringing the chilling tool into contact with dry ice. The chilling tool is then applied against the waste piece to cause the waste piece to thermally contract. This chilling tool also pushes against the waste piece to separate the waste piece from the rest of the work piece.
Japanese laid open publication 7-223828 criticizes the use of the 2-92837 chilling tool, and instead proposes the following method:
1. A scribe line is formed in a glass work piece with a mechanical scribing tool. This results in a crack that propagates partially through the work piece at an angle. The scribe line defines an inner portion of the work piece.
2. A portion of the work piece is heated (from the same side as the scribe line) to propagate the crack entirely through the thickness of the work piece. The crack propagates at an angle relative to the major surface of the work piece.
3. The inner portion of the work piece is pushed downward by a push rod, and separated from the remainder of the work piece.
In summary, the 2-92837 and 7-223828 references discuss mechanically scribing a glass work piece to form a crack in the work piece, and thermally propagating the crack through the work piece.
Another technique for scribing a glass work piece comprises using a laser to cut the work piece into a product piece and waste pieces. FIG. 1 illustrates a glass work piece 1 comprising cuts 2, 3 which extend through the thickness of work piece 1. Cuts 2, 3 separate work piece 1 into an outer waste piece 4, an inner waste piece 5, and a product piece 6 which is subsequently used as a substrate for the manufacture of a magnetic disk. Even though cuts 2, 3 extend through the entire thickness of work piece 1, one must still separate product piece 6 from waste pieces 4 and 5. This is difficult, because waste pieces 4, 5 contact and hold product piece in a manner that does not generally permit one to simply slide the product piece relative to the waste pieces. It is an object of this invention to provide a method for separating a work piece from one or more waste piece.
One problem with prior art break-out techniques is that they generate glass splinters and/or defects in the glass work piece. This reduces production yields. It is an object of some embodiments of the invention to minimize or reduce the number of splinters and/or defects generated when one separates a work piece from one or more waste pieces.
A method in accordance with a first embodiment of the invention comprises the step of providing a work piece including one or more cuts extending through the work piece. The cuts define a product piece and one or more waste pieces within the work piece. The product piece is separated from one of the waste pieces by providing a temperature difference between the product piece and the waste piece so that one expands relative to the other (and/or contracts relative to the other). This expansion (and/or contraction) facilitates separating the work piece from said one of the waste pieces.
In one embodiment, the work piece is a brittle material such as glass or glass ceramic. The cuts can be formed by applying radiant energy (e.g. a laser) to the work piece. Typically, a cooling fluid (e.g. a liquid or a gas) is applied to the work piece after application of the laser to form the cut, and ensure that it extends through the thickness of the work piece.
In one embodiment, the temperature difference between the product piece and the waste piece is greater than 125xc2x0 C., and preferably greater than 150xc2x0 C. However, the temperatures applied to the work piece should not be so extreme as to potentially damage or warp the work piece. Typically the temperature difference is between about 150 and 300xc2x0 C.
In one embodiment, the waste piece partially or completely surrounds the product piece. In such an embodiment, a temperature difference is provided such that the waste piece is hotter than the product piece, so that the waste piece is in an expanded state compared to the product piece.
In one embodiment, the temperature difference is provided by placing the waste piece against the surface of a heating element to thereby heat the waste piece. One or more channels are formed in the heating element that extend to the surface of the heating element against which the waste piece is placed. A vacuum is applied to the one or more channels to generate a force that holds the waste piece flush against the heating element to thereby prevent the waste piece from warping.
In another embodiment, the product piece partially or completely surrounds the waste piece. In such an embodiment, the temperature difference is provided such that the product piece is hotter than the waste piece, so that the product piece is in an expanded state compared to the waste piece.
A method in accordance with another embodiment of the invention comprises separating a product piece (e.g. a substrate used for the manufacture of a magnetic disk) from inner and outer waste pieces. In one such embodiment, the substrate is separated from the outer waste piece by heating the outer waste piece so that the outer waste piece expands relative to the substrate. The substrate (along with the inner waste piece) is then lifted (or lowered) relative to the outer waste piece to thereby separate the substrate from the outer waste piece. (Alternatively, the outer waste piece can be lifted or lowered relative to the substrate.)
Thereafter, the substrate is heated relative to the inner waste piece, and the inner waste piece is cooled relative to the substrate, so that the substrate expands relative to the inner waste piece, and the inner waste piece contracts relative to the substrate. Thus, a gap develops between the substrate and inner waste piece that facilitates separation of the substrate from the inner waste piece.
In another embodiment, the substrate is heated by placing the substrate in proximity to, but not in contact with, a heating element. Advantageously, this prevents the major surfaces of the substrate from being scratched during this process.
In one embodiment, the heating and cooling of the substrate and waste pieces is accomplished without physically contacting the data recording surfaces of the substrate.
After the substrate is separated from the inner and outer waste pieces, an underlayer (e.g. Cr, NiP, NiAl, a Cr alloy or other material), a magnetic alloy (e.g. a Co or Fe alloy) and a protective overcoat (e.g. carbon, hydrogenated carbon, or a ceramic material such as ZrO2) are deposited, in that order, onto the substrate to thereby form a magnetic disk. This can be accomplished by sputtering, evaporation, ion plating, or other vacuum deposition processes.